An RF inlay is generally understood to be an integrated circuit and antenna joined together on some type of substrate. Typically, the inlay is subjected to further processing to make a final product. Further processing may include adding additional outer layers of material such as plastic to make a card-shaped device. Other finishing techniques may form the inlay into a variety of final forms depending upon the final application of the product.
In general terms, the integrated circuit is inductively coupled to one or more interrogating devices or readers through the antenna by means of radio frequency communication. The integrated circuit or chip contains information that is useful for performing various tasks. One type of information is identification information pertaining to the holder or user of the RF device. In this case, the RF device may also be referred to as a radio frequency identification (RFID) device. Not all RF devices necessarily contain information about the identity of the user and some RF devices contain information in addition to the identity of the user.
RF inlays in their finished form are used in a variety of applications. For example, RF inlays are used for making security access devices (RFID devices) or may be used for other applications that may or may not involve identification of the user, including but not limited to access to computer or computer networks and databases, public transportation passes, toll way access passes, vending machine payment devices, and bank debit and/or credit cards and passports. Given the variety and expanding end user applications for RF devices, they are also sometimes referred to as “smart cards.” Some identification applications, such as passports, now utilize RFID inlays or RFID prelams (transponders that have been subjected to a lamination process) to store identification data and to allow efficient and rapid transfer of the identification data for processing by appropriate governmental agencies. The identification data may include biometric data, such as fingerprints, and/or photos of the passport holder, as well as information identifying the holder.
A variety of methods exist for manufacturing RF inlays. In some methods a substrate of one or more layers is processed in various steps including hot and/or cold lamination. A chip and antenna subassembly is incorporated in one or more of the layers and the layers are joined together by adhesives or by softening the plastic layer and, by means of pressure, joining the layers together. In other methods, wire is affixed to or embedded within a substrate in the form of an antenna and the opposing ends of the antenna coil are attached to the terminals of an integrated circuit (IC or chip) or to the terminal areas of a chip module. A chip module as that term is used herein comprises an integrated circuit attached to a lead frame having enlarged terminal areas. The terminal areas of the chip are connected to the enlarged terminal areas of the lead frame by either extremely small and delicate wires, on the order of 20 to 28 microns in diameter, or through a conductive adhesive such as in the case of a flip chip. The chip and the electrical connections to the terminal areas of the lead frame are encased in an epoxy layer for protection. The combination or subassembly of the chip/chip module and the coil of wire that forms an antenna is sometimes referred to as a transponder. The wire forming the antenna may be embedded fully or partially within the substrate by use of an ultrasonic wire embedding technique, as understood by those skilled in the art. The chip/chip module may be secured to the substrate by either placing it on the surface of the substrate or by placing it in a recess formed in the substrate. Adhesive may or may not be used to adhere the chip/chip module to the substrate. The ends of the coil of wire may be bonded or connected to the terminal areas of the chip or chip module at about the same time as the wire is embedded in the substrate, or the bonding may be done in a separate or subsequent manufacturing step.
Nominally, the wire used in the manufacture of RF inlays, where the wire is ultrasonically embedded in a substrate, is 110 to 120 microns in diameter, which includes an outer insulating layer. The wire is insulated to prevent short-circuiting of the antenna, as the windings of wire forming the antenna are closely positioned and may touch. The insulation layer is typically made from polyurethanes, polyvinylbutyrals, polyamides, polyesterimids and similar compounds. Thicker or larger diameter wires, compared to thinner or smaller diameter wires, are more easily handled and typically provide a farther read range when inductively coupled to a reader. Larger diameter wires are also more robust and are susceptible to removal from an RF device without damage to their integrity or the operation and functionality of the transponder. Potential removal and reuse of a transponder raises a number of security and privacy problems. For example, if a legitimate transponder subassembly (chip/chip module and antenna) may be removed from one passport and placed in another fraudulent passport, substantial security issues are raised.
There are a number of patents that disclose various devices and methods for the manufacture of RF devices including the manufacture of inlays. For example, U.S. Pat. Nos. 6,698,089 and 6,233,818 disclose methods of making an RF device wherein at least one chip and one antenna are affixed to a chip mounting board or substrate. The wire forming the antenna is embedded in the substrate by use of an ultrasonic generator. As part of the wire embedding process disclosed in each of these patents, the insulated antenna wire is first fixed to the substrate. The insulated wire is then guided directly over and away from a terminal area of the RFID chip and embedded to the substrate on the opposite side of the chip from the first embedding location to linearly align the wire between the two fixed locations and directly across the terminal area. Next, the antenna is formed by embedding the insulated wire into the substrate at a location spaced from the chip and terminal areas, the antenna being formed with a specific number of turns of the wire. The antenna wire is then guided over another terminal area of the RFID chip and finally embedded on the opposite side to anchor the second end of the wire directly across the other terminal area of the chip. The wire is then cut and the embedding head (or embedding tool) moves to a second transponder site on the substrate to repeat the same process. In the next stage of production, the wire portions passing directly over the terminal areas of the RFID chip are interconnected to the terminal areas by means of thermal compression bonding. Alternatively, the wire may be embedded as described and the chip subsequently positioned in a pre-designated recess where the terminals of the chip will contact the previously secured wire. The ends of the wire then will be bonded to the terminal areas of the chip by means of thermal compression bonding. U.S. Pat. No. 6,088,230 describes an alternative process where a first end of the wire is positioned in contact with a first terminal area of a chip or chip module and is bonded to the first terminal area, then the embedding tool embeds the wire in the substrate to form an antenna, and then the wire is positioned over a second terminal area of the chip or chip module where it is bonded to the terminal area.
While the inventions disclosed in these references may be adequate for the intended purposes, there is still a need for an improved method of making RF inlays for various applications including but not limited to contactless smart cards and other security access devices.
With respect to improved security for information stored on an integrated circuit incorporated within a transponder, it is desirable to improve fraud prevention. For example, with electronic passport devices it is desirable to inhibit the removal of a transponder from a valid passport such that the removed transponder cannot be used in a second fraudulent passport. In this regard, the present invention may utilize small diameter wire, for example 60-micron wire diameter or less. By using thinner wire, the ability to successfully remove a chip and antenna assembly from an existing product, such as a passport, is substantially reduced as the antenna and/or its connection to the chip or chip module will likely be destroyed upon any attempted removal. However, utilizing thinner wire also places a greater significance on the bond between the wire and chip terminals. When using thinner wire, flaws or defects in the bonding process can lead to weak and/or faulty bonds.
There is also a need to provide RF and RFID devices that have increased life and durability. One factor that limits the useful life of such devices is the quality of the electrical connection between the antenna wire and the chip. Improving the structural stability of the electrical connection or bond will necessarily extend the life of the transponder.
In this regard, another problem is that undesirable oxidation may occur over time due to impurities at the bond site. For example, insulation material on the wire or by-products of the insulation material created as part of the process of bonding insulated wire to the chip or lead frame terminal areas can form impurities at the bond site. More specifically, and as previously noted, the wire that is used to form the antenna often includes an outer insulation or coating. During a typical manufacturing process, the antenna wire is bonded to the terminal area or bond pad by a high-energy thermal compression bonding technique. The technique involves the application of a high voltage arc through a thermal bonding head that causes removal of the insulation, and simultaneously creates a localized weld that electrically connects the wire to the designated terminal. If all of the insulation is not removed from the wire the remaining insulation may reduce the quality of the electrical bond and, therefore, the quality of the electrical connection. Additionally, by-products of the insulation material formed from the high temperature bonding process may be captured within the bond and may cause oxidation or deteriorization of the bond over time. Current wire embedding techniques do not allow for precise localized removal of the insulation due to the potential of damaging the chip or chip module in the process resulting from the close proximity of the embedded wire and terminal areas. Indeed, as noted previously, prior art techniques lay the wire directly on top of the terminal areas of the chip as part of the wire embedding process. Additionally, a higher voltage is required to be used with thermal bonding process in order to accomplish both removal of the insulation and bonding of the wire to the terminal area than if the wire was insulated. As a result, the thermal bonding heads must be more frequently replaced, thereby increasing manufacturing costs, including a slowdown of production capacity while the heads are replaced. Moreover, even with complete removal of the insulation, a by-product or residue, such as hydrocyanic acid or other compounds, may remain at the bond site. It is believed that one or more of these residues may oxidize over time thereby further degrading the quality of the bond site and potentially shortening the life of the transponder.
It is therefore one object of the present invention to provide a method and apparatus for manufacturing RF and RFID inlays wherein fraud may be prevented by using a relatively thin wire antenna wire. Making the antenna wire of a minimum size makes removal of the antenna more difficult since the wire is more prone to breakage or damage during an attempted removal.
It is yet another object of the present invention to increase the life of RF and RFID devices wherein the quality of the electrical bonds between the antenna and chip bonding pads are improved by removing insulation from the wire prior to bonding, which also enhances the use of thinner antenna wire.
It is yet another object of the present invention to provide a method and apparatus of producing an RF or RFID inlay wherein known production equipment can be used to manufacture the inlay, thereby ensuring that the inlay of the present invention can still be incorporated within existing automated manufacturing processes.